Despite the increasing use of cellular telephone equipment, the traditional publicly-switched telephone network, or “PSTN”, continues to carry the bulk of local telephone communications in the United States. PSTN service is normally provided to the customers of a local exchange carrier, or “LEC” and is delivered over a PSTN telephone line to the customer's premises, referred to as the “local loop”.
Incoming call handshaking begins with a ring signal sent to customer premises over the PSTN local loop. In the United States, the ring signal is generally a 90-volt alternating current signal transmitted at 20 hertz, transmitted in a two second pulse every six seconds. Caller identification data, if available, is generally sent over the PSTN local loop between the first and second ring signal using a frequency-shift keying technique at 1,200 bits per second (1,200 baud). PSTN caller identification data generally includes the telephone number originating the call and a time and date stamp reflecting the current time. The data also commonly includes an ascii string of alphanumeric characters providing additional information regarding the call source.
A caller identification decoder attached to the PSTN local loop, which may be incorporated into a telephone or may be a separate unit, can decode the caller identification signal and provide the customer with information regarding the source of the incoming call. Generally, the decoder will incorporate some degree of memory for storage of caller identification information related to prior incoming calls in an incoming call log. Accordingly, a customer who has been away from the phone for some time can review the incoming call log and determine what phone numbers called that number and at what time. Certain telephone systems incorporate the capability to initiate a call to numbers stored in the incoming call log.
In addition to storing incoming call data in an incoming call log, certain telephone systems also store outgoing call data in an outgoing call log. Certain telephone systems incorporate the capability to redial numbers stored in the outgoing call log. These systems often incorporate a traditional redial function, which will automatically redial the number of the immediate prior outgoing call.